When your boiler stops working and a confusing error code flashes on the display, it can be both frustrating and worrying — especially during the colder months. But don’t panic. Many boiler fault codes are relatively minor and simply tell you or your heating engineer where to look first.
At Deakins Heating & Plumbing, we’re proud to be accredited installers of some of the most trusted boiler brands in the UK: Worcester Bosch, Vaillant and Ideal. To help you get to grips with what these codes mean, we’ve created a quick-reference guide to the most common boiler error codes by brand.
Understanding these codes won’t always mean you can fix the problem yourself — but it can give you peace of mind and help you pass on helpful info when booking a service call.
What Boiler Error Codes Actually Mean
Boiler fault codes are your system’s way of telling you something isn’t right. Some issues are simple fixes, like topping up low pressure, while others may need a qualified heating engineer.
The main types of boiler error messages are:
- Locking faults: These will stop your boiler from working until the issue is resolved and the system is reset.
- Blocking errors: These may stop heating or hot water for a period but can sometimes clear automatically.
- Maintenance alerts: These don’t usually stop your boiler but indicate something needs attention soon.
Below, you’ll find the most common codes and their meanings for Worcester Bosch, Vaillant, and Ideal boilers.
Worcester Bosch Boiler Fault Codes
Locking Errors (boiler will stop working until reset):
- EA – Ignition fault (can include frozen condensate pipe or gas supply issue)
- E9 – Overheating due to blocked heat exchanger or faulty temperature sensor
- E5 – Primary flow sensor overheating
- B7 – Control board needs replacing
- 9A / 9U – Issues with software components or code plug
Common Blocking Errors:
- A1 / No Code – Low water in the system. Check pressure gauge and repressurise to 1 bar.
- C1 / C6 / C7 – Fan issues
- EF – Temperature difference too large between flow and return
- 260 – Sensor disconnected or dry boiler
👉 Tip: Always try resetting the boiler once after checking the pressure gauge and bleeding any trapped air.
Vaillant Boiler Fault Codes
Vaillant boilers are popular for their reliability, but like any appliance, they can develop faults. Here are some key codes to watch out for:
- F75 – Very common. Often caused by low water pressure or a faulty pressure sensor. Topping up the system may help.
- F28 / F29 / F54 – Ignition or gas supply issues. Check your gas meter and supply.
- F62 / F61 – Gas valve faults. Needs engineer attention.
- F22 / F73 / F74 – Low water pressure or faulty pressure sensor.
- F83 / F84 / F85 – Implausible temperature readings, possibly due to incorrectly fitted sensors.
👉 F75 is the most frequent code we encounter with Vaillant systems — often just a case of needing a repressurisation or sensor reset.
Ideal Boiler Fault Codes
Ideal boilers are known for being user-friendly. Here’s what their most common fault codes mean:
- F1 – Low water pressure. Check the pressure gauge and top up if needed.
- F2 / L2 – Flame loss. Could be due to a blocked flue, faulty gas valve or temporary air in the system.
- F3 / F4 / F5 – Sensor or fan faults.
- L1 – Boiler overheating or no water flow. Check for closed valves or blockages.
- L5 – Too many resets. Indicates repeated unresolved issues — time to call an engineer.
How to Respond to a Boiler Fault Code
- Note the code exactly as it appears on your display.
- Check your boiler’s pressure gauge – many faults are simply due to low pressure.
- Consult your boiler manual or manufacturer’s website for model-specific advice.
- Try a reset – but only once and only if safe to do so.
- Contact a Gas Safe registered engineer – like Deakins – for expert support.
Still Unsure? Call Deakins Heating & Plumbing
Boiler codes can seem overwhelming, but they’re really just an early warning system. If your heating has stopped working or you’re seeing repeated fault codes, don’t delay. Call Deakins Heating & Plumbing and let our expert team take the stress away.
📞 Call us today on 01772 426 065
🌐 Or visit www.deakinsnw.co.uk to book an appointment online.
Stay Warm, Stay Safe
Regular servicing and quick action on error codes can prevent bigger (and more expensive) problems down the line. As your local boiler experts, Deakins are here to help — whether it’s a frozen pipe, a faulty sensor, or anything in between.